Wireless communication systems, such as the 3rd Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTS™), developed by the 3rd Generation Partnership Project (3GPP™) (www.3gpp.org).
The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Such macro cells utilise high power base stations to communicate with wireless communication units within a relatively large geographical coverage area. These base stations are called ‘NodeBs’, in 3GPP.
Typically, mobile/portable wireless communication units, or User Equipment (UEs) as they are often referred to in 3 G, communicate with a Core Network (CN) of the 3G wireless communication system. This communication is via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of Radio Network Subsystems. Each Radio Network Subsystem comprises one or more cells to which UEs may attach, and thereby connect to the network.
Lower power femto cells (or pico-cells) are a recent development within the field of wireless cellular communication systems. These lower power cells have a smaller coverage area than Node Bs. The term femto cells is used hereafter to also encompass pico-cells or similar.
Femto cells are effectively communication coverage areas supported by low power base stations, which may also be referred to as Home NodeBs (HNBs). These femto cells are intended for use within a relatively small area of the cellular network. They may support communications to UEs in a restricted, for example ‘in-building’, environment.
Typical applications for such femto Home NodeBs include residential and commercial, e.g. office, locations, and communication ‘hotspots’. In these uses, a Home NodeB can be connected to a core network of a communication system via, for example, the Internet. A broadband connection or the like may provide this connection. In this manner, femto cells can be provided in a simple, scalable deployment. They can be used in specific in-building locations where, for example, network congestion at the macro-cell level may be problematic. Significantly, the majority of HNBs are likely to be owned and deployed by members of the public, as opposed to a Network Operator owning a Node B.
Geo-location is the identification of the real-world geographical location of, say, a UE or the like. Geo-location of UEs can be performed in several ways. These include providing a UE with positioning equipment, such as GPS, or using network and mobile measurement data for nearby cells. A macro cell typically comprises a substantially unique Primary Scrambling Code (PSC) within its location area. A macro cell may therefore be distinguished from other macro cells, and thereby identified, based on its Location Area Code (LAC) and PSC. Accordingly, by identifying nearby macro cells for a UE, an approximate location of the UE may be determined, based on mobile measurement data for the identified macro cells. However, because of the relatively large coverage area of macro cells, this approach only provides some improvement in the degree of accuracy in identifying the location of the UE.
The use of femto cells for geo-location constitutes a special case. This is because femto cells have very limited range, unlike macro cells, and there can be many femto cells within the physical footprint of a single macro cell. Thus femto cells offer the potential for a higher degree of accuracy in identifying the locations of UEs. However, attempts to use femto cells for geo-location of a UE have tended to experience difficulties, for example:
(i) Femto cells are difficult to distinguish from one another in practice. This difficulty arises since they typically either share a single common Primary Scrambling Code (PSC), or a small number of shared PSCs. This can lead to considerable ambiguity in differentiating one femto cell from another.
(ii) The relatively small number of femto cells has meant that a UE is typically only in contact with a femto cell for much less time than it has a macro cell available. Hence designers have tended to favor geo-location methods that rely on macro cells, rather than femto cells.